The present invention relates to a packaging bag for housing foods or edible liquids which are to be heated in a microwave oven, or cosmetics such as warm packs.
In the prior art, when a food housed in a sealed packing bag is heated in a microwave oven, the packaging bag must be partly cut open with a pair of scissors or the like in order to prevent rupture of the bag which may occur when the internal pressure of the bag increases due to vapors arising from the heating.
Conventionally, a tool such as a pair of scissors, however, must be provided to partly cut the packaging bag open; this is disadvantageously cumbersome.
It is an object of the present invention to solve the above problem to eliminate the need to provide a tool such as a pair of scissors or the like for partly cutting a packing bag open and to allow the packing bag to be partly opened easily when the bag is heated in a microwave oven, based on an increase in the internal pressure thereof caused by vapors associated with heating.
The points of the invention for achieving this object are listed below.
1. A packaging bag made using as a material a synthetic resin film adapted for a microwave oven, wherein a layer constituting an inner surface is formed of a blend of a straight chain low-density polyethylene resin and a polybutene-1 resin, and one of opposite heat sealed portions perpendicular to a film flowing direction has a portion with a smaller heat seal width at an appropriate position.
2. The packaging bag according to claim 1, wherein the straight chain low-density polyethylene has a density between 0.915 and 0.950.
3. The packaging bag according to claim 1, wherein a blend ratio between the straight chain low-density polyethylene and the polybutene-1 is between 70:30 and 98:2.
4. The packaging bag according to claim 2, wherein a blend ratio between the straight chain low-density polyethylene and the polybutene-1 is between 70:30 and 98:2.
5. The packaging bag according to claim 1, wherein the bag is internally partitioned using partitioning heat sealed portions to form a plurality of spaces.
6. The packaging bag according to claim 5, wherein the straight chain low-density polyethylene has a density between 0.915 and 0.950.
7. The packaging bag according to claim 5, wherein a blend ratio between the straight chain low-density polyethylene and the polybutene-1 is between 70:30 and 98:2.
8. The packaging bag according to claim 6, wherein a blend ratio between the straight chain low-density polyethylene and the polybutene-1 is between 70:30 and 98:2.
This configuration provides a packaging bag that eliminates the need to provide a tool such as a pair of scissors for partly opening the packaging bag, wherein the layer constituting the inner surface of a film material constituting the bag is formed of the blend of the straight chain low-density polyethylene resin and the polybutene-1 resin, resulting in a difference in heat sealing strength between two perpendicular directions, so that when the bag is heated in a microwave oven, it can be partly opened easily due to an increase in the internal pressure thereof caused by vapors arising from the heating. Additionally, the packaging bag is internally partitioned using the partitioning heat sealed portions to form the plurality of spaces in order to house different types of contents in the corresponding spaces, so that when the internal pressure of the packaging bag increases, the partitioning heat sealed portions are released to mix the different types of contents in the corresponding spaces together.